Tabular: 

A plate-like structure in certain minerals.

Taconite: 

A highly abrasive iron ore.

Tailings: 

Material rejected from a mine or mill after most of the recoverable valuable minerals have been extracted.

Tailings pond: 

A low-lying depression used to confine tailings, the prime function of which is to allow enough time for heavy metals to settle out or for cyanide to be destroyed before water is discharged into the receiving watershed.

Talus: 

A heap of broken, coarse rock found at the base of a cliff or mountain.

Tamping: 

Compacting material over an explosive charge.

Telluride: 

A chemical compound consisting of tellurium and another element, often gold or silver.

Tenor: 

The relative value or mineral content of an ore.

Terrace: 

A relatively fiat area lying between the various levels of bench gravels.

Tertiary: 

The earlier of the two geologic periods in the Cenozoic era.

Thermal coal: 

Coal burned to generate the steam that drives turbines to generate electricity.

Thickener: 

A large, round tank used in milling operations to separate solids from liquids; clear fluid overflows from the tank and rock particles sink to the bottom.

Till: 

An unstratified and unconsolidated sediment deposited by glaciers.

Ton: 

Means a short ton (2000 pounds).

Tonne: 

Means a metric tonne (2204.6 pounds).

Tonnes-per-vertical-meter: 

Common unit used to describe the amount of ore in a deposit - ore length is multiplied by the width and divided by the appropriate rock factor to give the amount of ore for each vertical meter of depth.

Topography: 

The physical features of the surface in an area.

Tram: 

To haul cars of ore or waste in a mine.

Trammer: 

An electric train type engine used to move ore cars and other mining cars around in underground mining operations.

Transition zone: 

A zone containing a mixture of oxide and sulfide material, usually lying between the oxide and sulfide zones.

Trench: 

A long, narrow excavation dug through overburden, or blasted out of rock, to expose a vein or ore structure.

Trend: 

Direction or bearing of any rock formation.

Triassic: 

The earliest of the three geologic periods comprised in the Mesozoic era.

Trommel: 

A heavy-duty revolving drum and screen, utilized for washing, breaking up, and removing larger rocks and retrieving the sands and pebbles for processing in other placer recovery equipment.

Troy ounce: 

The most common unit of weight used to measure quantities of precious metals. One troy ounce equals 1.09714 avoirdupois ounces.

Tube mill: 

An apparatus consisting of a revolving cylinder about half-filled with steel rods or balls and into which crushed ore is fed for fine grinding.

Tuff: 

Rock composed of fine volcanic ash.

Tunnel: 

A horizontal underground opening, open to the atmosphere at both ends.

Tunnel-boring-machine: 

A machine used to excavate a tunnel through soil or rock by mechanical means as opposed to drilling and blasting.

Ultra basic: 

Igneous rocks containing less than 35% silica.

Umpire sample or assay: 

An assay made by a third party to provide a basis for settling disputes between buyers and sellers of ore.

Uncut value: 

The actual assay value of a core sample as opposed to a cut value which has been reduced by some arbitrary formula.

Unit Cost: 

The cost of producing one unit of commodity, such as an ounce of gold or a tonne of coal. The unit of measurement usually corresponds to how the commodity is priced in the market.

Unpatented claim: 

Usual lode, placer or millsite claim located under the mining laws.

Uraninite: 

A uranium mineral with a high uranium oxide content. Frequently found in pegmatite dykes.

Uranium: 

A radioactive, silvery-white, metallic element.

Upcast: 

A vertical ventilating shaft raising to the ground surface form an underground mine.

Upper lead: 

Pay gravel of pay streak in a gravel deposit that lies in strata well above bedrock.

Values: 

The valuable minerals contained in a deposit, usually refers to the precious metal content.

Vein: 

A fissure, fault or crack in a rock filled by minerals that have traveled upwards from some deep source.

Visible gold: 

Native gold which is discernable in a hand specimen by the unaided eye.

Volcanic Massive Sulfide: 

Mineralization in sulfide form (e.g. pyrite) containing a variety of metals such as zinc, lead, copper, silver, gold, cobalt and others (hence polymetalic) occurring in volcanic environments, i.e. rock originating from volcanoes.

Volcanic rocks: 

Igneous rocks formed from magma that has flowed out or has been violently ejected from a volcano.

Volcanogenic: 

A term used to describe the volcanic origin of mineralization.

Volume: 

A measurement of the amount of material in a placer, usually stated in cubic outwards.

Volume factor: 

A factor which takes into account the swell of loosened gravels after the material has been excavated. Most intact gravels swell at least 25 percent when they have been loosened.

Vug: 

A small cavity in a rock, frequently lined with well-formed crystals. Amethyst commonly forms in these cavities.

Wall: 

The sides of a mine working; rock on either side of an ore body.

Wall rocks: 

Rock units on either side of an orebody. The hangingwall and footwall rocks of an orebody.

Warrant: 

See rights.

Washing Plant: 

A processing plant to remove waste from coal or ore.

Waste: 

Mineralized or unmineralized rock that is not ore.

Water management: 

The process whereby the groundwater table in the mining area is lowered by pumping water from wells, and water is conveyed and used or recharged to the groundwater system through infiltration, reinjection or irrigation return.

Water table: 

The underground level at which the ground is saturated with water. The level at which water will stand in an excavation.

Wedge: 

A technique of directing a diamond drill hole in a desired direction away from its current orientation.

Wheat lamp: 

An electric light that mounts on a minerís hardhat for seeing underground. It is powered by a small lead-acid battery which is worn on a waist belt with a wire going to the headlamp.

Winnowing: 

A method of dry placer mining by using air.

Winze: 

An internal shaft.

Witness post: 

A claim post situated on a claim line used to take the place of a corner post that cannot be placed because of terrain.

Workings: 

Any mine excavation or operating areas.

Xenolith: 

A rock fragment of different composition enclosed in an igneous rock.

Yardage: 

The number of cubic yards of gravel contained in a placer deposit; also the number of cubic yards mined and processed per hour or per day.

Zircon: 

A durable, crystalline form of zirconium silicate that is commonly found in placer deposits.

Zone: 

An area of distinct mineralization.

Zone of oxidation: 

The upper portion of an orebody that has been oxidized.